In recent years, an electrochemical element, particularly a lithium secondary battery is widely used for power sources and electric power storage of small-sized electronic devices, such as cellular phones, notebook-size personal computers and the like and electric vehicles. There is a possibility that the above electronic devices and electric vehicles are used in a broad temperature range, such as high temperature in the middle of summer and low temperature in a severe cold season, and therefore they are requested to be improved in electrochemical characteristics at a good balance in a broad temperature range.
In particular, it is urgently required to reduce a discharge of CO2 in order to prevent global warming, and hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV) and battery electric vehicles (BEV) among environmental response vehicles loaded with electrical storage devices comprising electrochemical elements, such as lithium secondary batteries, capacitors and the like are required to spread in early stages. However, vehicles move at a long distance, and therefore they are likely to be used in regions of a broad temperature range from very hot regions in tropical zones to regions in a severe cold zones. Accordingly, the above electrochemical elements for vehicles are required not to be deteriorated in electrochemical characteristics even when they are used in a broad temperature range from high temperature to low temperature.
Lithium secondary batteries are constituted principally from a positive electrode and a negative electrode containing a material which can absorb and release lithium and a nonaqueous electrolytic solution containing a lithium salt and a nonaqueous solvent, and carbonates, such as ethylene carbonate (EC), propylene carbonate (PC) and the like are used as the nonaqueous solvent.
Also, metal lithium, metal compounds which can absorb and release lithium (metal simple substances, oxides, alloys with lithium, etc.) and carbon materials are known as the negative electrode. In particular, lithium secondary batteries produced by using carbon materials, such as cokes, artificial graphites, natural graphites and the like which can absorb and release lithium are widely put into practical use.
In the present specification, the term of a lithium secondary battery is used as a concept including as well a so-called lithium ion secondary battery.
In lithium secondary batteries produced by using, for example, highly crystallized carbon materials, such as artificial graphites, natural graphites and the like as negative electrode materials, it is known that decomposed products and gases generated from a solvent in a nonaqueous electrolytic solution which is reduced and decomposed on a surface of a negative electrode in charging the batteries detract from a desired electrochemical reaction of the batteries, so that a cycle property thereof is worsened. Also, when the decomposed products of the nonaqueous solvent are deposited, lithium can not smoothly be absorbed onto and released from a negative electrode, and the electrochemical characteristics thereof are liable to be worsened in a broad temperature range.
Further, in lithium secondary batteries produced by using lithium metal and alloys thereof, metal simple substances, such as tin, silicon and the like and oxides thereof as negative electrode materials, it is known that an initial battery capacity thereof is high but a nonaqueous solvent is acceleratingly reduced and decomposed as compared with a negative electrode of a carbon material since a micronized powdering of the material is promoted during cycles and that battery performances, such as a battery capacity and a cycle property are worsened to a large extent. Also, in a case the micronized powdering of the negative electrode material and the deposition of the decomposed products of the nonaqueous solvent are deposited, lithium can not smoothly be absorbed onto and released from the negative electrode, and the electrochemical characteristics thereof are liable to be worsened in a broad temperature range.
On the other hand, in lithium secondary batteries produced by using, for example, LiCoO2, LiMn2O4, LiNiO2, LiFePO4 and the like as a positive electrode, it is known that decomposed products and gases generated from a solvent in a nonaqueous electrolytic solution which is partially oxidized and decomposed in a local part in an interface between the positive electrode material and the nonaqueous electrolytic solution in a charging state detract from a desired electrochemical reaction of the batteries, so that the electrochemical characteristics thereof are worsened as well in a broad temperature range.
As shown above, decomposed products and gases generated when a nonaqueous electrolytic solution is decomposed on a positive electrode or a negative electrode may interfere with a migration of lithium ions or may swell the battery, and the battery performance is thereby worsened. In spite of the above situations, electronic equipments in which lithium secondary batteries are mounted are advanced more and more in multi-functionalization and tend to be increased in an electric power consumption. As a result thereof, lithium secondary batteries are advanced more and more in an elevation of a capacity, and a nonaqueous electrolytic solution is reduced in a volume thereof occupied in the battery, wherein the electrode is increased in a density, and a useless space volume in the battery is reduced. Accordingly, observed is a situation in which the electrochemical characteristics thereof in a broad temperature range are liable to be worsened by decomposition of only a small amount of the nonaqueous electrolytic solution.
It is shown in a patent document 1 that the cycle property at room temperature is excellent when sulfonic ester represented by iso-propyl methanesulfonate is added to a nonaqueous electrolytic solution.
It is shown in a patent document 2 that the cycle property at room temperature is excellent when sulfonic ester represented by methyl methanesulfonate is added to a nonaqueous electrolytic solution.
It is shown in a patent document 3 that the cycle property at 20° C. is excellent when a disulfonic ester compound represented by propylene glycol dimethanesulfonate which has two sulfonate groups and has certainly a side chain on a principal chain is added to a nonaqueous electrolytic solution.
It is shown in a patent document 4 that the cycle property in charging the battery so that an open circuit voltage in completely charging the battery is higher than 4.2 V is excellent when a disulfonic ester compound represented by 1,4-butanediol dimethanesulfonate which has two sulfonate groups and in which a principal chain is a linear alkylene chain is added to a nonaqueous electrolytic solution.
A nonaqueous electrolytic solution containing a silicon compound, such as 1,2-bis(3,5-difluorophenyl)-1,1,2,2-tetramethyldisilane and the like is proposed in a patent document 5, and it is suggested that the cycle property at 60° C. and the low-temperature properties are improved.
Also, a nonaqueous electrolytic solution containing a silicon compound having an alkyl sulfonate group, such as trimethylsilyl methanesulfonate and the like is proposed in a patent document 6, and it is suggested that the cycle property at 25° C. and the trickle charging property are improved.